The aminoacylation of bacterial polysaccharide antigens and its biological role are poorly understood, although it might be relevant in infection and immunity. Due to the lability of ester-linked substituents on glycoconjugate antigens, such groups usually escape detection during routine structural investigation. Of the few data available, those on the occurrence of glycine in the endotoxic lipopolysaccharides of Gram-negative bacteria are well documented. This article summarizes these data on glycine as an integral constituent of bacterial LPS and also some other amino-acid esters in the teichoic acids and phosphatidylglycerol of Gram-positive bacteria. The possible functions of such noncarbohydrate ester-linked substituents in bacterial antigens are discussed. Because glycine, an inherent component of bacterial lipopolysaccharides in the core region, is supposed to participate in epitope formation, such a structure may be considered for potential use in the construction of a vaccine with broad specificity.